The use of optical and/or optoelectronic devices is increasing in communications applications. These devices can include a variety of components that make use of electro-absorption media such as silicon-germanium (SiGe). These components include components such as modulator and light sensors. The composition of the electro-absorption medium used in these components typically affects the performance of the component. For instance, the ratio of Si:Ge in SiGe can affect the modulation wavelength of a modulator. However, the composition of these electro-absorption media is often difficult to control. The composition is even more difficult to control when different components on a single device each use an electro-absorption medium with a different composition. As a result, there is a need to control the composition of the electro-absorption media included on optical devices.